#include <algorithm>
#include <iostream>
#include <vector>
#include <numeric>
using namespace std;

vector<int> prime_table(int n) {
    vector<int> is_prime(n + 1);
    if (n) iota(is_prime.begin() + 2, is_prime.end(), 2);
    for (int i = 2; i * i <= n; i++) if (is_prime[i]) {
        for (int j = i + i; j <= n; j += i) is_prime[j] = 0;
    }
    return is_prime;
}
vector<int> make_primes(int ma) {
    vector<int> ps = prime_table(ma);
    ps.erase(remove(ps.begin(), ps.end(), 0), ps.end());
    return ps;
}

int main() {
    int n; cin >> n;
    vector<int> dp(n + 1, -1);
    dp[0] = 0;
    for (int p: make_primes(n)) {
        for (int i = n; i >= p; i--) if (dp[i - p] == -1) {
            dp[i] = max(dp[i], dp[i - p] + 1);
        }
    }
    cout << dp.back() << endl;
    return 0;
}